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Research and development on hydrothermal liquefaction (HTL) of wet microbial biomass have been on a dramatic rise. Although microalgae have been the main feedstocks, investigations of HTL of yeast species were few, not to mention yeast biomass cultivated on cellulosic hydrolysates. In this study, six catalysts were tested regarding their effects on yields of biocrude and biochar from partially defatted Cryptococcus curvatus. Among the six, K2CO3 at 350 and 300 °C and KOH at 350 °C led to the highest yield of biocrude, 68.9%, 63.9% and 67.0%, respectively. These biocrudes had low content of sulfur and nitrogen but high HHVs in the range of 36.9 and 39.0 MJ/kg. The biocrudes from the top three running conditions were dominated by fatty acids and fatty acid esters based on GC/MS identification. The corresponding aqueous phase samples contained high concentrations of fatty acids among all that were identifiable. The successful HTL of the partially defatted yeast cell residues promises a platform where lignocellulosic sugars can be converted to biodiesel from yeast cell lipids and biocrude from the remaining yeast cells.

Biogasifying coal to methane represents an environmentally benign way to utilize the abundant and inexpensive coal resource. To increase methane yield from coal, numerous studies have investigated the approach of biostimulation through finding the best nutrient solutions to enhance microbial activities. Toward this end, however, almost all studies have adopted laboratory made medium that is tap water- or deionized and distilled water- based. As a matter of fact, this water is dramatically different from formation water in coal basins. Thus, in order to enhance methane release from coal in situ, this study aimed to design a formation water-based recipe. To accomplish this objective, the chemical and microbial compositions of the formation water collected from the San Juan basin were analyzed first. Equipped with this fundamental knowledge, a screening test was conducted to evaluate nine parameters to identify statistically significant ones affecting methane yield from coal. For those critical parameters, the optimal value for each was determined through response surface methodology. Finally, the predicted results by the models were verified by an experimental study adopting all optimum conditions. This study demonstrated that microbes capable of converting coal to methane were present at the San Juan basin and the developed recipe increased methane yield 24.3-fold compared to those without.

Microalgae have been widely researched and are proven to be a promising feedstock for biodiesel production. Tremendous efforts have been made on microalgal biology, strain screening, cultivation, harvesting, and postharvest processing. Strategies for commercialization are under development by optimizing the overall utilization of microalgae for both biofuels and value-added bioproducts. In this chapter, the fundamentals of microalgae as a feedstock for biodiesel production are illustrated. Strain selection and cultivation requirements are considered from the processing aspects. Methods and technologies of preconversion preparation, including dewatering and drying, cell rupture and lipid extraction, are discussed. Novel processing processes, such as in situ methanolysis under sub/supercritical methanol conditions, are also covered to reflect the advancement in microalgal biodiesel production. This chapter is intended for readers who have had some technical background in microalgal lipids-based biodiesel, and as a reference for college students and other technical personnel in the fields of biofuels, bioresources, and other related fields.

For the purpose of producing biocrude from pretreated and washed sweet sorghum bagasse, hydrothermal liquefaction (HTL) was conducted with six different catalysts at two temperatures. The six catalysts were: K2CO3, KOH, formic acid, Ni/Si Al, Ni2P and zeolite. The two temperatures were 300 and 350 °C. Based on two selection criteria, high yield of biocrude and low yield of biochar, K2CO3, KOH, and Ni/Si Al were identified as the best catalysts which led to biocrude yields of 61.8%, 42.3% and 45.0% at 300 °C, respectively. As the best catalyst, K2CO3 led to biocrude samples with higher heating values (HHVs) of 33.1 MJ/kg. This biocrude had high carbon content and low contents of nitrogen and sulfur based on elemental analysis. However, the relatively high content of oxygen around 15% requires the biocrudes to be upgraded before refinery ready. Key compounds identified in these biocrudes will assist future effort in upgrading. Overall, this study proved that the pretreated bagasse is a suitable feedstock for HTL for generating biocrude. Through a simple dilute acid pretreatment step and HTL of the resulting solid, every component of sorghum bagasse can be used for producing biofuels.

Phospholipids and free fatty acids (FFA), along with triglycerides, are naturally formed constituents in unrefined vegetable oils and other plant lipids. Presence of phospholipids and FFA in such oils can cause processing difficulties, such as saponification and decrease in catalytic efficiency, thus lead to an adverse process efficiency in the transesterification of such oils for biodiesel production. This phenomenon was also observed in our previous study on converting microalgal lipids to fatty acid methyl esters (FAME) via in situ transesterification. This study aimed at further exploring the transesterification of phospholipids and investigating the effects of FFA presence and other processing conditions in biodiesel production from plant oils in sub- and/or super-critical methanol (SubCM/SCM). Experiments were carried out in a batch reactor in SubCM/SCM under various conditions without addition of catalysts. Pure chemicals of lecithin and stearic acid were used as the model compounds for phospholipids and FFA, respectively. The product yield (FAME in mol%) of the phospholipids after transesterification, as affected by the presence of FFA under different conditions, was selected as the respond factor to determine the process efficiency. Experimental results showed that phospholipids can be converted into FAME in such a process. Transesterification of phospholipids is largely affected by the interactive effect of operating temperature and reaction time. The increase in product yield is proportional to the increases in temperature and/or reaction time. The maximum product yield of 68.1 mol% was achieved at 250 °C and 120 min without the presence of FFA. The product yield started to level off once the system reached the SCM state. When temperature was held at 290 °C for 30 min, the product yield dropped to 33.6 mol%. Another phenomenon observed is that the presence of FFA enhances considerably the lipid conversion. The study revealed that phospholipids can be converted to FAME with a highest product yield of 93.9 mol% at 250 °C for 120 min in SCM without catalysts and with the presence of FFA. However, the FFA enhancement became less significant when the system was operated for a longer period of time than 120 min.

Microalgae are considered as one of the most promising feedstocks for biofuel production because of their environmental and social benefits. However, challenges exist in converting microalgal lipids into algal biofuels because of the unique characteristics of microalgae and the technologies for processing them. This study aims at exploring an alternative sub-/supercritical methanol (subCM/SCM) process technology that combines lipid extraction from whole microalgae and lipid esterification/transesterification in a single step or in situ transesterification. A high lipid content microalgal strain, Schizochytrium limacinum, was used for in situ transesterification in a batch reactor. Temperature (170, 210, 250, and 290 °C), reaction time (30, 60, 90, and 120 min), and lipid/methanol molar ratio (sRatio; 1:50, 1:75, and 1:100) were investigated for their effects on the conversion efficiency. The temperature appeared as a most positive influential factor. Additionally, the operating temperature over 250 °C cau...

It is now widely accepted that microalgae are promising candidate feedstocks for biofuel production, especially for biodiesel. Microalgae consist of a vast number of species that contain complex chemical constituents and physical structures. The purpose of this study is to understand the physical and chemical properties of selected microalgae, which is critical to the design of appropriate processes for commercial biofuel production. ASTM standard methods were implemented to examine the microalgae properties, including proximate and ultimate analyses. Among the microalgae studied, green microalgae have more volatile matter than brown microalgae, while the latter contain much higher ash content (as high as 43.4%wt ±0.20%wt dry basis). The lowest ash content was found in the samples of green microalgae (14.3%wt ±0.10%wt dry basis). Ultimate analysis showed that brown microalgae have less carbon content (approx. 25%wt dry basis) as compared to green microalgae (49%wt to 58%wt dry basis). All samples of microalgae were high in sulfur content (0.4%wt to 1.0%wt dry basis). Mineral contents of all microalgal samples were similar to those commonly present in other biomass. Brown microalgae contain significantly higher amounts of carbohydrates (72.9%wt to 75.5%wt dry basis) than green microalgae. On the other hand, green microalgae contain more crude fat (17.1%wt to 27.8%wt dry basis) than brown microalgae. The fatty acid profiles show that the primary fatty acids in microalgal lipids are similar to those of vegetable oils such as soybean oil. However, there are also many odd-numbered fatty acids, such as C15:0, C17:0, and C19:0, which are not typically seen in other seed oils.